The Aims of this project are a direct answer to the mission of the NIMH to address the epidemiology of postpartum depression, to identify associated risk factors and characterize child developmental and mental health outcomes associated with clinically significant postpartum mood change. Postpartum depression is the most common complication of childbearing (Wisner KL, Chambers C, Sit D. Postpartum depression: A major public health problem. JAMA 2006~296:2616-2618), evident in approximately 11%-19% of all new mothers (Evidence Report / Technology Assessment 119. AHRQ Publication 05-E006-2). To date, most research on postpartum depression has relied on small convenience samples from clinics or hospitals that cannot generate normative data and utilize varying diagnostic criteria that more often focus on depressive symptomatology rather than clinical diagnoses of depression. This study builds on the unique resources for research on mental health available in Sweden. Linking a constellation of Swedish registers, including the National Patient Registers of health and health service utilization, National School Register, National Pharmacy Register, Total Population Register and Housing Census, we will: (a) expand upon the current knowledge base of the epidemiology of postpartum depression by more accurately describing the magnitude and pattern of clinically significant postpartum depression (hospitalized and non-hospitalized) and associated risk factors and~ (b) comprehensively characterize the child development outcomes of maternal postpartum depression. We will utilize advanced statistical methods to identify the developmental consequences of postpartum depression assessing which children of postpartum depressed mothers are more or less likely to develop problems, whether explained by maternal characteristics, such as depression timing, severity, subtypes (with and without psychosis) or comorbid conditions, child characteristics such as gender, or contextual factors such as poverty. The aims of the study are ambitious, but we have established a team of international experts with a long history of collaboration, which is well suited to address the study Aims. For predictive purposes, evaluating a comprehensive set of potential determinants of postpartum depression will generate new insights to help predict, identify, and ultimately help to prevent and treat this disorder. Because the period immediately following the birth of a child is a critica time and postpartum depression constitutes a serious threat to the infant's well-being, the epidemiologic characterization of clinically significant postpartum depression and its associated impact on childhood developmental outcomes is the first necessary step in developing adequate treatment plans.